Lactic Acid Bacteria and Immune System Modulation

Lactic acid-producing bacteria promote a healthy immune system.

Lactic acid bacteria are normal residents of the human GI tract and exert many beneficial effects, notably on the immune system. The use of some specific bacteria as probiotics is now well established. As such, they provide beneficial health effects to the host, by helping balance the gut flora.

Many of the benefits of probiotics used in foods and as supplements are a consequence of the capacity of these microorganisms to stimulate and modulate the host immune system.1 But how do lactic acid bacteria exert these beneficial effects?

The mechanisms responsible for the beneficial effects of lactic acid bacteria used as probiotics appear to be multifactorial. The intestine plays a primary role in the healthy functioning of the immune system. Activation of the immune response involves the coordinated efforts of the intestinal flora, mucosal immune cells and epithelial cells. Epithelial cells act as a critical barrier to potentially undesirable organisms entering via the oral route. The intestinal flora stimulates a local response at the intestinal wall. This mucosal immune function is an important element of the individual’s immune system because it is responsible for maintaining an appropriate balance between mounting a defense against undesirable invaders and inducing tolerance to environmental and dietary antigens.1 Probiotic bacteria have been shown to help the immune system respond (for example, by increasing secretion of IgA) and to help barrier function (by decreasing gut permeability).

In addition, lactic acid bacteria, including the genera Lactobacillus and Bifidobacterium, produce lactic acid from carbohydrates through the process of fermentation, thus lowering the pH level in the intestinal tract. It is this acidification process which is one of the most beneficial effects of lactic acid bacteria; the drop in pH in the GI tract can be sufficient to inhibit the growth of acid-sensitive microorganisms, including many undesirable ones. 1, 2

To be effective, species of Lactobacillus and Bifidobacteria must reach the intestine intact following oral administration. This requires that these microorganisms not only survive production and storage, whether as food or supplement, but also must stand up to the rigors of passage through the gastric and pancreatic environments. On reaching the intestine, these beneficial microorganisms must be able to establish themselves, at least transiently, remain viable, and carry out their normal metabolic activities to contribute to a beneficial balance of intestinal flora.

Infant diet and immune system modulation
Oral administration of lactic acid bacteria via foods or supplements has been shown to be well tolerated and safe at all ages.

One study compared the effects of two types of formula on infants’ fecal pH versus fecal pH of a control group of breastfed infants. One formula was supplemented with Bifidobacteria; the second formula was a standard unsupplemented formula. Both breastmilk and the probiotic-supplemented formula yielded a higher number of infants with Bifidobacteria in their stools at one month of age, than did the standard formula group. And, in both the breastmilk and the probiotic-supplemented formula groups, fecal pH was also significantly lower (i.e., more acidic) than that in the unsupplemented-formula group. 4

Lactic acid bacteria used in a probiotic application thus support a healthy immune system in a variety of ways.

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